The present invention relates to a method and apparatus for generation and ejection into air of discrete agglomerations of particulate material with a proportion of liquid from a liquid having the particular material therein. Such a method is disclosed in WO-A-93/11866 (PCT/AU92/00665) and includes providing the particulate material to an ejection location, applying an electrical potential to the ejection location to form an electric field and causing agglomerations to form at the ejection location. The agglomerations are ejected away from the ejection location by electrostatic means.
In order to control the ejection of agglomeration and particles the electrical potential needs to be varied from below a threshold to above a threshold. However, it has been found that, in certain constructions, it is difficult to achieve full control and true drop-on-demand performance. The present invention sets out to overcome this problem.